A group from Stanford University, etc. has reported that small noncoding RNAs are the third scaffold of glycosylation.
https://pubmed.ncbi.nlm.nih.gov/34004145/
Existence of glycosylated RNAs (named GlycoRNAs) was confirmed with the following protocol. Authors metabolically labeled cells with peracetylated N-azidoacetylmannosamine (Ac4ManNAz), and RNA was extracted with warm TRIzol, then ethanol precipitated, desalted via silica columns, stripped of protein contamination via high concentration proteinase K digestion, and repurified over silica columns. After RNA purification, Ac4ManNAz was conjugated to DBCO-biotin, visualized with streptavidin-IR800 (Strep), and imaged on an infrared scanner.
The RNA scaffolds for glycosylation was found to be small noncoding ones. Most of glycoRNAs existed on cell surface, and GlycoRNAs were modified with complex-type N-glycans with at least one terminal sialic acid residue. It was found that these GlycoRNAs directly bind to Siglecs.
The framework in which glycobiology is presently understood excludes RNA as a substrate for N-glycosylation. This discovery of glycoRNA suggests the current view is incomplete and points to a new axis of RNA glycobiology, including as of yet undiscovered biosynthetic and trafficking mechanisms. Further, it highlights the possibility that cell surface glycoconjugates, which mediate and regulate important inter-cellular interactions.